This invention relates to methods employing piezoelectric oscillators for detecting members of specific binding pairs.
A piezoelectric oscillator in common use as a frequency standard in electronic equipment typically consists of a quartz crystal, cut in a particular plane in the shape of a thin wafer and having a layer of metal deposited on each of the two larger parallel planar surfaces as electrodes.
When placed in an appropriate oscillator circuit, the crystal vibrates at or extremely near its natural or native frequency of vibration. It is well known that coupling a mass to the surfaces of such a piezoelectric oscillator causes a shift downward in the vibrational frequency of the oscillator, and that the amount of change in frequency is related to the amount of mass. This relationship between the mass coupled to the oscillator and the frequency shift forms the basis for using such an oscillator as a mass sensor, or so-called piezoelectric microbalance, as described in W. H. King, 1964, Anal. Chem., vol. 36(a), pages 1735-39.
A. Shons et al., J. Biomed. Mater. Res., vol. 6, pages 565-70, describes using a piezoelectric microbalance to determine the quantity of a given antibody in a solution, by coating the crystal surface with an antigen specific for the antibody and measuring the vibrational frequency, then exposing the antigen-coated surface to the antibody in solution to allow formation of the specific antigen-antibody binding pairs, and then again measuring the vibrational frequency and computing the mass of bound antibody from the frequency shift.
T. K. Rice, 1980, U.S. Pat. No. 4,236,893, describes determining a particular class of antibody by exposing a surface of a piezoelectric oscillator, previously coated with an antigen specific to the antibody, to a test solution containing an unknown amount of the antibody, allowing the antibody to bind to the antigen, and then exposing the surface to a sandwiching substance which selectively binds to the specific subclass of the antibody being determined. The amount of the specific subclass bound on the oscillator (and thus in the test solution) is related to the shift in vibrational frequency resulting from the addition of the sandwiching substance. T. K. Rice, 1982, U.S. Pat. No. 4,314,821, describes determining the amount of an immunologically-reactive substance in a liquid test solution containing interfering material that can bind to an antigen by contacting a surface of a piezoelectric oscillator, previously coated with an antigen specific to the antibody, to the test solution, allowing any of the antibody that may be present in the test solution to bind with the antigen, and then exposing the surface to an excess of a substance specifically reactive with all of the bound antibody and not with the interfering material. The amount of the antibody bound on the oscillator (and thus in the solution) is related to the shift in vibrational frequency resulting from the addition of the specifically reactive substance.
N. Flowers et al., 1986, Fed. Proc., vol. 45(6), page 1516, describes detecting a target single-stranded nucleic acid in a test solution by contacting the test solution with a surface of a piezoelectric oscillator, upon which a complementary single-stranded nucleic acid was immobilized, to allow hybridization of the complements. The amount of the target nucleic acid specifically bound on the oscillator (and thus in the test solution) is related to the shift in vibrational frequency resulting from the mass increase owing to the addition of the target nucleic acid.